Ultrasound Case of the Month

THE CASE

You are a mid-year R3 and are starting to feel pretty good about running the resuscitation bay. As you sip your morning coffee thinking about the recent trauma arrest and medical resuscitations you crushed, the Telemetery Phone rings… “Medic 164 coming in with a woman in her mid-20s and we think she might be in labor. She’s contracting every 1-2min and she’s pretty darn uncomfortable. I think this baby is coming soon doc. We are about 5 minutes out. Oh, and she says she hasn’t been seen for this pregnancy yet.” While you get your ED team assembled in the bay and prepare for a possible precipitous delivery, your mind starts rushing though all the labor complications your patient may be at risk for given her lack of prenatal care. Just as your palms have reached maximal dampness, your attending steps in and suggests “Hey, why don’t you grab an Ultrasound so we can see what we’re dealing with.”…

The LABUR protocol

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Early obstetric point of care ultrasound (POCUS) remains one of the core emergency ultrasound (US) applications with ample evidence supporting its usefulness in detecting intrauterine pregnancy, fetal heart rate, and gestational age [1]. While early pregnancy complaints commonly present to the emergency department (ED), precipitous delivery is a much less frequent ED presentation and remains an area of discomfort for many ED providers [2]. POCUS can quickly provide information to help guide decision-making during precipitous delivery, thereby improving provider confidence and comfort. The Labor Assessment with Bedside UltrasonogRaphy (LABUR) protocol described below is one method to quickly evaluate both mother and fetus in preparation for precipitous delivery. 

Figure 1. 'Sign of the cross’ pattern used for initial scout scan

The exam is best preformed with the patient in a supine position using a curvilinear  3.5-5 MHz probe. An initial scout scan should be preformed in two planes (longitudinal and transverse) over the maternal uterus in a ‘sign-of-the-cross’ pattern (Figure 1).  The longitudinal scan should proceed from the pubic symphysis to the uterine fundus and the transverse scan from one lateral edge of the uterus to the other. After the initial scout scan, attention can be directed to each of the five scan components:

Fetus(es)
“Is there in fact a fetus in the uterus?”
There are times when patients are not able to answer questions. Additionally, false pregnancy (pseudocyesis), delusion of pregnancy, and feigned pregnancy are rare but extremely helpful to rule out.
“How many fetuses are there?”
This can be a surprisingly challenging question to answer especially after rupture of membranes (ROM) and loss of amniotic fluid as an acoustic window. The fetal skull serves as a recognizable landmark that can be used to determine gestational number in this situation. To ensure that fetal crania are not missed, the entire maternal abdomen should be scanned in the transverse plane in a ‘mowing-the-lawn’ pattern (Figure 2). 

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Figure 2. ‘Mowing the lawn’ pattern used to assess fetal crania, placenta and amniotic fluid

Fetal Presentation
“Where is the fetal head located?”
Cephalic presentation is confirmed when the fetal skull is visualized in the maternal pelvis. However, even when the skull is located in the pelvis this could still represent a possible compound (aka head and hand/arm) or funic (umbilical cord) presentation. If the fetal head is found elsewhere, the provider should be prepared for a possible breech or shoulder delivery (Figure 3). 

Figure 3. Sweep of the uterus - the fetal head can be seen initially with the cranium a distinct rounded hyperechoic shape. The chest can been seen next and finally the abdomen.


“How close is the fetal head to the pubic symphysis?”
If the fetus is found to be cephalic, determining how far the head had progressed into the maternal pelvis can help determine imminence of delivery. The relationship of the fetal skull to the maternal pelvis is best viewed in the longitudinal plane with the probe placed directly over the center of the pubic symphysis (Figures 4 and 5). If the fetal head has not yet crossed a vertical line perpendicular to the inferior pubic symphysis, the fetus is at least a station of -3 (closest fetal part 3cm above the ischial spine) or higher [3]. As the distance between the fetal skull and the inferior pubic symphysis boarder shortens, so does the time until delivery [4].

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Figure 4. Appropriate probe placement to evaluate relationship between fetal crania and pubic symphysis

Figure 5. Ultrasound image showing fetal crania and inferior pubic symphysis. In this clip, note the fetal head as a rounded hyperechoic line on the left side of the screen. The pubic symphysis is a similarly hyperechoic line with a dense shadow that is placed in the near field on the right side of the screen.

Amniotic Fluid Assessment
“Is amniotic fluid present?”
Amniotic fluid appears anechoic on ultrasound evaluation, though late in pregnancy floating debris can be seen. Lack of amniotic fluid in the setting of precipitous delivery is highly suggestive that ROM has already occurred. However, presence of amniotic fluid does not rule out ROM as it often takes time for all/majority of the amniotic fluid to be lost.
“How much fluid is present?”
Measurement of the maximal vertical pocket (MVP) is used to quantify amniotic fluid volume and is the preferred method due to simplicity of measurement and lower false positive rate for oligohydramnios (low amniotic fluid level) [5]. With the transducer in the transverse plane, scan the entire abdomen in the ‘mowing-the-lawn’ pattern to look for the deepest vertical fluid pocket that is free of fetal parts and umbilical cord. Once located, the pocket is measured vertically in centimeters. Normal MVP is 2-8cm [5]. Oligohydramnios (MVP <2) can be caused by a variety of reasons, one of which is previous ROM.

Placenta
“What is the location of the placenta relative to the cervix?”
Evaluation of the placenta is the least precise and most challenging aspect of the LABUR exam. First, obtain a general idea of where the placenta is located in the uterus by moving the probe in the transverse plane in a ‘mowing-the-lawn’ pattern described above (Figure 2).  The placenta may be located on any uterine surface, therefore it is important to scan the entire uterus in this manner (Figure 6 and 7).

Figures 6 and 7. Ultrasound clips of the placenta. The placenta is a relatively homogenous isoechoic structure within the uterus. In these two clips you can see a fundal placenta.

Figure 8. An example of Placenta previa. Note the isoechoic placenta inferiorly placed.  It occupies the entire lower uterine segment. 

If possible, the distance between the lower edge of the placenta and internal cervical os should be measured by placing the probe in the transverse plane at the inferior edge of the placenta. If this distance is >2cm placenta previa, marginal placenta, and low lying placenta are ruled out. However, during a precipitous delivery the cervical os is frequently unable to be visualized due to dilation, uterine contractions falsely decrease the distance between the placenta and the os, and the location of fetal parts low in the pelvis can obstruct a clear view of the placental edge. A posteriorly located placenta can be particularly difficult to visualize as fetal parts make a poor acoustic window. For better visualization of a posterior placenta, the probe can be moved laterally along the maternal abdomen. In general, if the placenta can be visualized in the anterior fundal position, placenta previa is highly unlikely (Figure 8).

Fetal Heart Rate
“What is the fetal heart rate?”
Determination of fetal heart rate (FHR) is commonly evaluated via emergency provider POCUS during all stages of pregnancy. Once a view of the fetal heart is obtained (Figure 9), M-mode is used to place the line of interest across the beating heart (Figure 10). This then creates an image of that line over time, highlighting movement. The heartbeat can be seen as the up-and-downward movement of cardiac tissue over time. FHR is then calculated either peak-to-peak or trough-to-trough. Normal baseline FHR during labor is defined as 110-160 bpm. However, it is important to note that FHR is dynamic and undergoes regular accelerations and decelerations during labor thus a one-time measurement must be interpreted with caution.

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Figure 10. M-mode to calculate Fetal Heart Rate (FHR) via 2 beat peak-to-peak method

Figure 9. Ultrasound view of fetal heart.



Next steps for your learning…

Maneuvering the probe around a fetus to identify fetal parts can be very challenging for new learners of point-of-care ultrasound. One helpful maneuver is to “anatomy link.” First, find the head. It is easily identifiable. Once the head is located, find the spine. It appears as a set of parallel hyperechoic lines when in long axis or a hyperechoic circular shape in short axis. Use the spine to locate ribs or the pelvis.

Though it isn’t a part of the traditional LABUR protocol, gestational age estimation is a very helpful skill to have in your toolkit for this situation. Because there are so many ins and outs to it, we’ll save it for another post!

CASE RESOLUTION

Your patient arrives by EMS and does indeed appear quite uncomfortable. You are ready with Ultrasound in hand and while completing the LABUR protocol you discern that this is her first pregnancy, she has felt baby moving actively, her water broke about 2 hours ago and she has had no bleeding. You find one fetus that appears to be cephalic with its head above the pubic symphysis and you finally exhale knowing you likely have at least a little time. There is very little amniotic fluid present and you see the placenta towards the fundus of the uterus. While your teams gets access you call your OB colleagues and let them know you will be sending a patient upstairs to Labor & Delivery. Later that morning she delivers a healthy baby boy.

Take home points

  • Precipitous delivery is a relatively rare and often high-risk ED presentation

  • Point of care ultrasound can provide key information during a precipitous delivery to help guide decision making

  • The LABUR protocol quickly evaluates the featus (number, presentation, heart rate), amniotic fluid (presense, quantity), and placenta (location) in late gestation


Authored by Brittney Bernardoni, MD

Peer Reviewed by Lori Stolz, MD, RDMS

References

  1. Ultrasound Guidelines: Emergency, Point-of-care, and Clinical Ultrasound Guidelines in Medicine. American College of Emergency Physicians. June 2016.

  2. Janicki AJ, MacKuen C, Hauspurg A, Cohn J. Obstetric training in Emergency Medicine: a needs assessment. Med Educ Online. 2016 Jun 28;21:28930. 

  3. Youssef, A., et. al. Fetal head–symphysis distance: a simple and reliable ultrasound index of fetal head station in labor. Ultrasound Obstet Gynecol. 2013 Apr;41(4):419-24. 

  4. Ghi, T., et. al. Sonographic pattern of fetal head descent: relationship with duration of active second stage of labor and occiput position at delivery. Ultrasound Obstet Gynecol. 2014 Jul;44(1):82-9. doi: 10.1002/uog.13324. Epub 2014 May 28.

  5. Robert Jones, DO FACEP & Jessica Goldstein, MD FACEP. “Point-of-Care OB Ultrasound.” American College of Emergency Physicians, 2016.